1. Field of the Invention
The present invention relates to communication systems. More particularly, the present invention relates to a method and apparatus for selecting one or more users from among several users for access to communication services in a code division multiple access system.
2. Description of the Related Art
Communication access in system may be provided to one user at a time. Therefore, when a first user is granted access to the system, other user must wait until the first user has released the system; then access is granted to a new user. A scheduler may select the new user among the users waiting for access to the system. Each user may send a request for access to the scheduler. The scheduler then selects the new user from among the users that have made a request for access.
In a code division multiple access system (CDMA), access may be granted to several users at the same time over the same channel frequency. Access may be granted to the users based upon several criteria. The first criteria may relate to the type of services that each user has subscribed with the communication system. Access is provided to each user based on the priority of the subscribed services. For example, a user may request constant bit rate (CBR) service, variable bit rate (VBR) service, or available bit rate (ABR) service. Users with CBR service are guaranteed to receive communication services at the subscribed data rate (i.e., bit rate). In contrast, for users with VBR services, the users are provided communication services at the rate necessary to transmit the information. In such cases, the user's fees are typically calculated based upon the rates that were requested and granted to the user. If the user pays for ABR service, then the user is granted access at a data rate that is available at the time of access. In an order of priority, if there is sufficient capacity in the system to also provide access to an ABR user, then the ABR user is granted access at an available data rate. In one aspect, the capacity of the system is typically dependent upon whether the amplifier in the transmitter is capable of transmitting the ABR user's information with sufficient power without overdriving the amplifier in light of the amount of power required by each of the CBR and VBR users' power requirements. The available data rate at which the access is granted depends upon the amount of power that is available for transmitting the ABR user's data. An example of an ABR user is in case of an Internet Service Provider (ISP). Since customers of an ISP are able to tolerate delays and lower data rates, an ISP may typically select the less expensive ABR service. Moreover, there are frequently situations in which there is insufficient power to transmit data for all of the ABR users that are requesting ABR service at any particular point in time. Therefore, the transmitting station may determine to which ABR users service is to be provided in an order of priority.
Several techniques are known for determining how to select a user for access to a communication system in a shared access communication system in which access is granted to only one user at a time or to a few users that are less than all of the users requesting service. Access to a system may be provided to a user by one or more channels (i.e. air interface links between a common transmitting station and the user). Accordingly, each user may be associated with at least one channel. In a CDMA system, each channel is associated with a unique CDMA code. Typically, the condition (i.e. quality) of the channel directed to each user is changing over time. Furthermore, the condition of the channels varies from user to user. Access may be granted to the user that can use the system most efficiently. Such a user is associated with the best channel condition that is able to receive data at the highest rate. As such, the throughput of the communication system is maximized. The throughput of the system may be measured in terms of the amount of data communicated by the system over a period of time. Access may also be granted such that each user is provided with essentially equal access to the system over a period of time. Equal access may refer to either the fact that each user may receive an equal amount of time to communicate over the system, or that each user may transmit/receive an equal amount of data over a period of time.
The scheme in which the most efficient system user gets access and the scheme in which equal access is provided to each user are deficient. The scheme that focuses on maximizing throughput may lead to a situation in which some users receive minimal opportunity to access the system. The scheme in which each user is given equal access is also unacceptable due to the resulting inequitable distribution of access for different types of services. Moreover, in schemes in which each user is granted equal access regardless of the ability of that user to efficiently use the system, the throughput of the system suffers.
Accordingly, there is a need for a method and apparatus for determining to which user to grant access in a shared access communication system, such that the throughput of the system is maximized while ensuring that each user is granted equitable access to the communication system.